DNA barcoding to identify fish species is being used by the US Food and Drug Administration (FDA) to tackle potential substitution.

The results are on a public database of barcodes for commercial seafood on the FDA website, used by regulators, private laboratory scientists on behalf of seafood suppliers, and academic researchers.

Tests create the barcodes, which look like the lines of different thicknesses on Universal Product Code (UPC) labels used to identify and scan manufactured products.

However, unlike these barcodes, they will not be attached to the product.

Sequencing DNA of the fish

Sequencing the DNA in a fish sample would provide too much information but scientists can identify one specific piece of DNA that has just 650 bases. That fragment typically provides enough genetic information to identify a fish species.

Once a fish species is identified in FDA labs, the newly created barcode unique to that species is entered into a database, making up a library or catalogue of commercial fish species.

When encountering a fish or fish product (fillets, fish sticks, sushi, etc.) whose species is unknown, inspectors with the equipment can create a barcode for that fish and compare it against FDA's database to seek a known match.

Photo: FDA/Michael J. Ermarth fish

The agency has trained more than 20 analysts to use the procedure in its regional field laboratories and is now performing the analysis.

Scientists at the Canadian Centre for DNA Barcoding have proposed creating a portable device so that the process can move beyond the laboratory.

“The current library contains 300 species of fish. The sequences are from specimens collected by FDA or donated by collaborators such as NOAA’s National Marine Fisheries Service and the Florida Department of Agriculture,” Jonathan Deeds, research biologist at FDA's Center for Food Safety and Applied Nutrition, told FoodQualityNews.com.

“The FDA is currently assessing the extent of seafood species substitution (i.e. intentionally substituting one species for another) within the complete seafood distribution chain (from import, to processing, to distribution, to retail).”

Deeds said the agency was not able to offer a timeline when the work will be complete.

FDA has worked with the Smithsonian to get fish for sequencing and about 1,200 specimens have been collected.

“Each specimen needs to be preserved, authenticated, vouchered into the National Fish Collection at the Smithsonian, and sequenced before it can be added to the FDA library,” he said.

“Many specimens are nearing the end of this process and should be added to the library this year.”

How it works

When a fresh fish arrives at FDA labs, a small piece is removed and its DNA is tested, the nucleic acid that carries genetic information, and a larger piece saved in case of future sampling.

The piece is stored for long-term use in freezers at ultra-low temperatures of -80 degrees Celsius.

The remainder of the whole fish is sent to the Smithsonian for authentication and indefinite safekeeping.

FDA is expanding its seafood identification capabilities to include commercial decapod crustaceans (shrimp, crab and lobster).

A DNA testing method for the crustaceans is being validated and a reference library is being constructed which is expected to be completed within a year.

Previous methods for fish species identification included visual inspection of external identification markers and the isoelectric focusing of proteins.

The current DNA analysis takes one to two days to complete which is more of a challenge for perishable, fresh (not frozen) fish.

FDA said that DNA evidence has already been used by FDA in support of enforcement actions against fish wholesalers found to be substituting one fish for another.

“In 2013 the Department of Justice charged the owner of an Illinois seafood distributor with mislabeling fish. The owner subsequently pleaded guilty and received a maximum $100,000 fine and was sentenced to five years' probation.”

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